This invention relates to a controller for a mobile structure such as a power window of an automobile that can be opened and closed and more particularly to such a controller that can reliably prevent such a structure from operating erroneously when, for example, the automobile has fallen into a body of water and the controller is in an underwater condition.
In general, power window systems for an automobile are electronically controlled and provided with a function of automatically reversing the window motion for preventing an object such as a person's had from becoming caught by the closing window. Control units of the type adapted to control the source power supplied to a motor serving as the actuator of a window to control its motion are commonly each provided to a seat of the automobile, each comprising a motor-driving circuit with relays for rotating the motor in two directions and a control circuit including a microcomputer for controlling these relays in response to the user's switch operations. A function for making communications among the control units may be provided such that a specified one of the control units at one of the seats such as the driver seat can control the opening and closing of all of the windows including the windows at the other seats. In other words, communication lines may connect the control units for different windows such that the driver may be able to operate a knob on his/her controller unit on the elbow rest on the door on his/her side such that signals can be transmitted to the other control units to open and close windows corresponding to the other seats such as the passenger seat or a back seat. Such control units are sometimes called an operation unit because operation switches to be operated by the user are usually integrally incorporated.
From the point of view of safety, it is important for such power window systems to function reliably even when the automobile has sunk into a body of water such that the system will not operate incorrectly because of a leak current due to the presence of water or an error in the microcomputer and also that it will not become impossible to open the windows from inside.
Japanese Patent Publication Tokkai 2000-179234 describes an operation unit provided with a detecting circuit for detecting an underwater condition adapted to switch on both relays of the motor-driving circuit of this operation unit if an underwater condition is detected thereby such that both terminals of the motor come to be at a same potential and the motor is prevented from moving in an unwanted direction. Its circuits are further so structured that if the user attempts to open a window, say, by manually operating a switch while an underwater condition is being detected by the detecting circuit, both terminals of the coil of the relay for closing the window will come to be at a same potential such that the motor will turn in the direction of opening the window.
Japanese Patent Publication Tokkai 2000-179234 describes two types of systems with control units at different seats connected with a bus line for multiplex communications provided with measures to be taken under an underwater condition. Systems of one of these types may be characterized as having the operating units of different seats connected by a signal communicating line separate from the aforementioned bus line and a detecting circuit for an underwater condition incorporated into one or all of the operation units such that if any of the detecting circuits detects an underwater condition, the detection circuit which detected the underwater condition outputs a detection signal to each relay of the other operation units through the signal line, thereby providing a voltage similar to the source voltage to forcibly switch on each relay of each operation unit.
Systems of this type are disadvantageous because a separate signal line is required for the application of voltage for driving the relays besides the bus line for communications among the units. Thus, the wiring becomes complicated and the production cost of the vehicle to which the system is mounted is increased.
Systems of the other type may be characterized as having a detection circuit incorporated in the operating unit at one or all of the seats such that if any of them detects an underwater condition, the operating unit incorporating the detection circuit that detected the underwater condition transmits a detection signal to the other operating units and that the control circuit of each operating unit that receives this detection signal forcibly switches on each relay within that operating unit. With a system thus structured, if any of the seats is immersed in water, erroneous operations of the windows at all seats due to the underwater condition can be prevented.
Systems of this type also have problems. Firstly, signal waveforms of the multiplex communications are likely to be disturbed by electric leaks and attachment of a conductive object to the connector terminals on the boards of the operation units under water and this may inhibit transmission of correct detection signals. Secondly, such electric leaks and attachment of a conductive object may cause an overcurrent through the CPU of the microcomputer of the control circuit. If the CPU is thereby damaged and fails to function properly, it is again likely that the detection will not be transmitted correctly. If the operating unit of a seat such as the driver's seat has gone under water, a detection signal may be transmitted from this operating unit due to a current leakage into the bus line and the windows by the other seats corresponding to operating units not yet under water may start to open or close erroneously in response to such a signal.